1. Field of the Invention
The present invention relates to micro position-control systems and, more particularly, to a micro position-control system capable of more precisely controlling three degree-of-freedom motions, namely, a Z-direction motion, an X-axis rotation, and a Y-axis rotation.
2. Description of the Related Art
As is well known, the importance of micro position systems in industry increases day by day. Particularly, the development of semiconductor technology requires a high integration of a circuit, and consequently, a line width used in up-to date microprocessor circuits is about 0.18 μm. In this case, a motion stage for manufacturing a wafer requires precision that is reproducible corresponding to 20 nm, which is 1/10 of the 0.18 μm line width. A submicron-level micro transfer apparatus is widely utilized, and can be applied to a micro measurement field (such as, an atomic force microscope (AFM), a scanning electron microscope (SEM), and the like) and to an industrial field, such as, information technology (IT).
General position-control systems using a linear motor or both a servo motor and a ball screw have a relatively long stroke distance but have a limit to the position precision that can be achieved due to a structural limit, such as a backlash or the like. Also, general position-control systems have a drawback of becoming high due to vertically arranging actuators for the purpose of obtaining vertical motion. This drawback causes much difficulty in performing a vertical position control in works that require high precision.
Micro-precise position-control systems that move by a distance of micrometers or less must be designed to not generate friction in order to remove or minimize a non-linear factor. Also, actuators used in the micro-precise position-control systems must be easily driven through a distance of micrometers or less and must be highly repetitive.
Hence, in the field of micro position-control technology, a position control technique using the piezo effect is generally used. The piezo effect denotes a phenomenon in which when a piezo actuator is deformed by an external force applied to a special crystal of the piezo actuator, voltage is generated on a surface of the piezo actuator, and alternatively, when voltage is applied to the crystal, a displacement or a force is generated. Examples of materials that produce such a piezo effect include crystal, tourmaline, titanium, barium oxide, and the like. The piezo effect is applied to micro position-control technology, electroacoustic transducers, piezoelectric purification, supersonic humidifiers, fish finders, supersonic diagnostic devices, and the like.
Korean Patent No. 396020 (hereinafter, referred to as a related patent) discloses a conventional position-control system using the piezo effect, whose structure is shown in FIG. 1. In FIG. 1, a first transfer mechanism 30 (with piezo actuator 31), a second transfer mechanism 40 (with piezo actuator 41), and a third transfer mechanism 50 (with piezo actuator 51) can create translation in the X and Y directions and rotation in the Z direction. Also, when a fourth transfer mechanism 60, a fifth transfer mechanism 70, and a sixth transfer mechanism 80 deform piezo actuators by applying a voltage to the piezo actuators, a motion in the Z-direction occurs because of a lever structure of FIG. 2. A motion stage 20 having six degrees of freedom is formed by combining the six transfer mechanisms 30, 40, 50, 60, 60, 70, and 80 together.
The motion stage 20 is manufactured to have six degrees of freedom in a relatively simple shape. Each hinge is made circular, and hinges of six degrees of freedom are simultaneously attached to a single moving object.
Referring to FIGS. 1 and 2, the fourth, fifth and sixth transfer mechanisms comprise a piezoelectric actuator 61, 81, 71 a first hinge 62, 72, 82 a second hinge 63, 73, 83, a fixing block 64, 74, 84, a third hinge 67, 77, 87, and a lever 68, 78, 88 which make the motion stage 20 translate along a Z-axis, which corresponds to a vertical motion, and rotate around the X-axis and Y-axis. The first, second, and third transfer mechanisms 30, 40, and 50 interlock with the fourth, fifth, and sixth transfer mechanisms 60, 70, and 80, and make an X-axis translation, a Y-axis translation, and a Z-axis rotation, respectively, so that the motion stage 20 can make six degree-of-freedom motions with respect to the base 10.
In the related patent, first, a thin circular hinge portion is prone to be deformed in all directions as well as being bent. Hence, the rigidity and stability of the entire system are very poor.
Second, since ends of all piezo actuators are simultaneously fixed to the motion stage 20, a parasitic motion in which motions in all directions affect one another occurs. Hence, a precise operation of the position-control system is difficult. In other words, to move the motion stage 20 in a specific direction, inputs that enter all drivers must be either calculated simultaneously or calculated through feedback control. Thus, control is difficult.
Third, since the thin hinge portion receives a large force directly from piezo actuators, the thin hinge portion is very likely to be broken or plastically deformed even by a small external force.
Fourth, since the lever structure of FIG. 2 rotates about a hinge 63 instead of making a perfect vertical motion, the lever structure causes a motion in an undesired direction. Finally, since the system is not designed to perform displacement amplification, a moving range of the motion stage 20 is restricted to a deformation range of a piezo actuator in which the piezo actuator can only extend about 0.1% of its length.
The manufacture of a plane motion stage having degrees-of-freedom including an X-direction translation motion, a Y-direction translation motion, and a Z-axis rotation is easy because of manufacturing characteristics of an elastic hinge mechanism used in an existing micro position-control system. However, the manufacture of a plane motion stage having degrees-of-freedom including a Z-direction translation motion, an X-axis rotation, and a Y-axis rotation is not easy because wire electro-discharge machining, which is generally used to manufacture an elastic hinge, cannot achieve three-dimensional machining, it can only achieve two-dimensional machining.
In addition, although a stacked piezo actuator, which is frequently used as a driving source of a micro driving mechanism, has great driving power and excellent resolving power of several nanometers or less, the stacked piezo actuator has a drawback in that its deformation range is limited to about 0.1% of the overall length of the actuator. Accordingly, when a motion stage needs to move in the Z-direction, its height increases. Therefore, there is a demand for an elastic hinge mechanism that can decrease an overall height of a motion stage and also generate a large displacement in the Z-direction.